I didn't - I attached one split ring to the webbing on the top/outside of the pack, and for the front pocket I attached the ring to the zipper pull. It's not as elegant as an interior O-ring, but I liked my pack enough to want to keep using it (rather than getting a new Bihn pack, which may still happen in the future! ).
But the key ring trick has come in handy for other, non-TB bags (like some of my knitting project bags for which TB doesn't offer a comparable size) where I still want to use TB accessories. Or when I have a lot of straps that I want to attach to a single O-ring - then I use the key ring as a way to expand the capacity of the O-ring.